Electroslag Welding (ESW) and Electrogas Welding (EGW)
Electroslag welding is quite similar to vertical submerged arc welding. The essentials of electroslag welding are shown in Fig. wherein two plates (A) and (B) having thickness (C) are welded one pass. This joins the workpieces by casting the filler metal between the butted edges of the workpieces being joined and the joint is made in one pass. A granular flux is placed in the joint gap between the two plates being welded.
During welding, the molten metal and slag are retained in position in the joint with the help of a pair of copper shoes (water cooled), which move automatically upwards as welding progresses. In the first instance, the arc is started between the electrode tip and the bottom portion of workpiece. The flux added which gets melted by arc heat. With the melting of flux, a blanket of slag is formed (and covers the bottom tip of electrode) and the are (between electrode and workpieces) goes out.
The current is later conducted directly from electrode wire through the slag and thus the high resistance offered by the slag is responsible for causing most of the heating for the remainder of the welding process. Electroslag welding is used for welding hot rolled carbon steels, low alloy high strength steels and other thicker sections (50 to 900 mm thickness) with welding speeds up to 36 mm/minute. The process is used for fabrication and building of heavy machines and nuclear reactor vessels and other structures. Current used may be up to 600 amperes.
The process is quite automatic as once started, it will keep going till the welding is completed full length. Warping is minimum as heating is uniform. No joint preparation is required. The process of electrogas welding is similar in principle to electroslag welding with the difference that an inert gas is used for shielding purposes. The process is used for welding in one pass the edges of structural sections as also the circumferential welds with plate thickness varying from 12 to 75 mm.
Inert gases used for shielding include carbon dioxide, argon or helium based on the type of material to be welded. Single or multiple flux-cored electrodes are fed to welding zone where a continuous arc is maintained during welding. The shielding gas may be provided from an external source or from flux-cored electrodes.
Electroslag welding set-up.
Electrogas welding finds application for welding steels, aluminium alloys, titanium, etc. for the construction of pressure vessels, bridges, large diameter thick walled pipes, storage tanks and for building ships.
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